let a = [1, 2, 3, 4];
b = a;
b.reverse();
console.log(a);

let num1 = 3;
let num2 = new Number(3);
let num3 = + "3"
console.log(num1 == num2)
console.log(num1 === num2)
console.log(num2 == num3)
console.log(num2 === num3)

console.log('200000' > '21000')
console.log(+true)
console.log(!'cupdata')

// 考察箭头函数
const circle = {
  radius: 10,
  perimeter () {
    return 2 * Math.PI * this.radius
  }, 
  diameter: () => 2 * this.radius 
}
console.log(circle.perimeter())
console.log(circle.diameter())

console.log(name);
console.log(age);
var name = '小美';
let age = 20;